The present invention, generally relates to thermal management for electronic devices, and more particularly to apparatus for reducing the occurrence of condensate on thermal management devices.
The performance of electronic circuits and their semiconductor devices is limited by temperature. Semiconductor device performance degrades when the internal temperature reaches or exceeds a particular limit. That limit depends upon the nature of the semiconductor device. In order to maintain or increase the performance of such devices, they must be cooled in some way. The manner of cooling depends upon many parameters, including the space available for the cooling process, the temperatures to be encountered, etc. In some instances simply passing a fluid over the device or, over a finned heat sink that is attached to the device, is sufficient to maintain the semiconductor at safe operating temperatures.
In one known semiconductor device cooling technique, convecting fins are attached to a semiconductor package, or the package is affixed to a larger metal member, referred to as a heat sink or cold plate. This heat sink draws heat away from the semiconductor device and can be air cooled or liquid cooled, depending upon the particular application. If the heat sink is air cooled it will typically have heat convecting fins.
Different cooling fluids may be used, when liquid cooled methods are employed, depending upon the application and the density of the electronic devices in a given circuit. Boiling liquids are often used, such as fluorinated hydrocarbon refrigerants, which are delivered to the cold plate in liquid form and are boiled to remove heat. These systems often have the highest heat removal rate for a limited xe2x80x9ccold platexe2x80x9d area, but require a considerable amount of power to operate, i.e. to be pumped to and from the heat transfer site.
Under certain circumstances, moisture from the ambient environment may condense on the heat sink or cold plate. In the case of liquid-cooled heat sinks, there are periods of time during which the temperature of the heat sink may fall below the temperature of the surrounding environment, often referred to in the art as xe2x80x9csubambientxe2x80x9d operation. This condition may occur any time the surface temperature of the heat sink falls below the ambient air temperature. When this subambient operation condition occurs, moisture from the surrounding atmosphere may condense on the outer surface of the heat sink. The condensed moisture collects and runs off of the heat sink and into contact with the circuit board, semiconductors and packages, and other components. This free liquid can cause significant damage to those components and degrade the overall performance of the electronic device, or even destroy it all together.
There is a need for a thermal interface system, positioned between a semiconductor package and its associated heat sink, that will reduce or prevent condensation from forming in appreciable quantities.
In a preferred embodiment, a thermal jacket is provided that reduces the condensation of moisture during subambient operation of a cooled heat sink by increasing the temperature difference between the surface of the heat sink and the surface of the thermal jacket. The thermal jacket includes a bonding layer positioned in substantially surrounding and overlying relation to the cooled heat sink, at least one porous layer positioned in substantially surrounding and overlying relation to the bonding layer, a barrier layer positioned in substantially surrounding and overlying relation to the at least one porous layer; and a sealant layer positioned in substantially surrounding and overlying relation to the barrier layer. Advantageously, the at least one porous layer traps air close to the surface of the heat sink so as to provide a thermally insulating air barrier between the surface of the heat sink and the ambient environment.
A method for forming a thermal jacket positioned in overlying and substantially surrounding relation to a cooled heat sink is also provided, that reduces the rate of condensation of moisture during subambient operation of the cooled heat sink. The method comprises the steps of applying a bonding layer to the outer surface of the cooled heat sink; applying at least one porous layer to the bonding layer; applying a barrier layer to the porous layer; and applying a sealant layer to the barrier layer.